In modern bicycles, in particular in high performance ones, it is spreading the use of on-board equipment that uses hydraulic controls. This is the case for example of hydraulic disc braking systems, in which the force necessary to obtain a suitable braking by means of the closing of the braking calipers on the discs is too high to be able to be easily exerted with the normal cable systems, controlled by the hands of the cyclist. With these braking systems, therefore, the effort exerted by the hand of the cyclist is transferred to a hydraulic group; more specifically, a piston is actuated that pressurizes oil inside a cylinder. The pressurised oil is then transferred through suitable tubes to the brake calipers, to obtain the braking.
As well as the disc braking systems, also other equipment could usefully use a hydraulic control. In particular, with reference again to the braking system, hydraulic rim braking systems are also known, in which braking calipers act on the rim of the bicycle wheel, and not on discs like in the previous case.
There are also known integrated control devices of the hydraulic brake and of the gear, front and rear (i.e. acting on the toothed wheels of the crankset of the bicycle and, respectively, on the sprockets of the sprocket assembly mounted on the rear wheel).
In any case, the control devices of the hydraulic brake are generally mounted at the two ends of a bicycle handlebar, and act on the braking of the front and rear wheels.
Document EP 2749487 discloses a hydraulic brake control device, integrated with a control device of mechanical gear (i.e. the actuation of which is of mechanical type).
The brake and gear actuators are mounted on a housing body comprising a handgrip portion and an attachment portion to the bicycle handlebar. In particular, the brake actuator comprises:
a brake lever hinged on the housing body through a pin;
a hydraulic cylinder wherein a piston is slidable that is kinematically connected to the brake lever through a connecting rod and a shaped plate, an end of the connecting rod being pivoted to said piston and the opposite end acting on the shaped plate, the shaped plate being associated with the brake lever;
a return spring provided between the piston and an inner wall of the cylinder;
a tank for hydraulic fluid in fluid communication with the hydraulic cylinder.
The hydraulic cylinder and the tank are made in one piece with the housing body, in particular the housing body provides a substantially cylindrical cavity that defines the inner walls of the cylinder wherein the piston slides and that houses the contrast spring.
Document US 2012/0240715 discloses a hydraulic brake control device, in which the brake actuator is mounted on a housing body comprising a handgrip portion and an attachment portion to the bicycle handlebar. In particular, the brake actuator comprises:
a brake lever hinged on the housing body through a pin;
a hydraulic cylinder wherein a piston is slidable that is kinematically connected to the brake lever through a connecting rod, an end of the connecting rod being pivoted to said piston and the opposite end being associated with the brake lever;
a return spring provided between the piston and an inner wall of the cylinder;
The hydraulic cylinder is made on a hydraulic unit that is hidden inside the housing body, and can be made in one piece with the housing body itself. In any case it is provided a covering case—made from rubber, plastic or light alloy—that covers the housing body and consequently also the hydraulic cylinder.
The Applicant has found that the aforementioned control devices of the hydraulic brake have various drawbacks.
Firstly, the aforementioned hydraulic brake control devices have a difficult maintenance for the hydraulic components (in particular for the piston and tank), since—in order to access them—it is necessary to dismount and remount the outer walls of the housing body and of the covering case (in the case of the device according to US 2012/0240715).
Another drawback found by the Applicant for the device according to EP 2749487 is linked to the use of the kinematic mechanism formed by connecting rod and shaped plate as connections between piston and brake lever. Such a kinematic mechanism must be mounted with precision and only a part of the force exerted by the user on the brake lever reflects onto the piston along its axis, whereas a substantial part of the force exerted by the user is dispersed in the kinematic mechanism itself.